wow…you’re going to have to be verrrrrrrrrrrry careful here. Switching to even a low calorie diet will probably cause weight gain initially. I’d be looking at 1200 calories a day and see how your body reacts. Then, if all seems to be going well, add 100 calories a week to your diet until the balance starts to shift back to weight gain (if that doesn’t happen right away). The only thing that will really help here is exercise in order to offset the effects of introducing carbs back into your diet. Hopefully you’re already exercising 30 to 40 minutes a day on this low carb program. If not, strap on the running shoes or you’re libel to see a rapid weight gain even on a low cal plan. Have a look at this site it might give you some ideas…good luck..